Electron gun having a segmented control electrode



Dec. 12, 1967 w. E. GLENN. JR

ELECTRON GUN HAVING A SEGMENTED CONTROL ELECTRODE Filed Dec. 18, 1964 In van to r Wil/idm E. Glenn Jrr, bywh/mf' His Attqr'ney.

United States Patent ELECTRON GUN HAVING A SEGMENTED CONTROL ELECTRODE William E. Glenn, Jr., Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed Dec. 18, 1964, Ser. No. 419,429 4 Claims. (Cl. 313-83) ABSTRACT OF THE DISCLOSURE A grid structure is provided for an electron gun in which the electron beam aperture is defined by four mutually insulated grid sections which are energized to provide beam centering. The opposed grid sections are energized by direct current voltages of adjustable magnitude which are respectively above and below the grid voltage for controlling the intensity of the electron beam,

so that adjustment of the centering voltages does not disturb the intensity control.

gun usually includes a small beam limiting aperture, and

with such a structure very accurate alignment of the grid and cathode electrodes with the anode aperture are required to avoid collecting an excessive portion of the electrons on the anode in the area surrounding the beam limiting aperture. In accordance with an important aspect of the present invention, an improved grid structure providing for a centering adjustment of the electron beam in the limiting aperture is provided.

Accordingly, it is'an important object of the present invention to provide a simple electron gun structure which provides a focused beam centered in the limiting aperture of the anode.

It is another object of the invention to provide an improved electron gun structure for producing a high intensity beam of small cross section.

It is a further object of my invention to provide an improved electron gun structure for providing a high intensity beam of small cross section which does not require an excessive degree of accuracy in manufacture and assembly.

Further objects and advantages will become apparent as the following description proceeds, reference being had to the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing,

FIG. 1 is an elevational view in section of an improved electron gun structure embodying my invention;

FIG. 2 is an exploded view in perspective showing the details of construction of the gun structure of FIG. 1; and

FIG. 3 is a schematic representation of an energizing circuit for the electron gun structure of FIG. 1.

Referring now to the drawing, I have shown in FIG. 1 an elevational view in section of an improved electron gun embodying my invention and including a filamentary cathode 10, an anode 11 and an interposed, segmented grid structure 12. The cathode is of a refractory metal, preferably tungsten, and is bonded to a pair of rigid lead-in conductors 13 and 14, which are sealed through a ceramic header 15. The lead-in conductors may be hoe formed of tantalum or other refractory metal. The anode in the specific form illustrated is preferably a disc-like member of titanium bonded on one face to one end of a ceramic cylinder 16. The other end of the ceramic cylinder is bonded to an outwardly extending flange 17 of the grid structure 12. The grid structure as a whole, is of a generally cylindrical configuration and is made up of four segments 18-21, inclusive, each forming essentially a quarter of the cylindrical structure and preferably being formed by slotting a cylindrical member. The grid structure defines a central aperture 22 into which the end of the filamentary cathode 10 extends. The portion of the grid facing the anode is generally hemispherical in shape and cooperates with a generally conical portion 23 of the anode, which extends toward the grid from the anode member and is of gradually reducing cross section. The beam passage 24 is formed centrally of the anode and at the other end is an accurately dimensioned disc-like insert 25, preferably of molybdenum, having an accurately dimensioned electron beam limiting aperture 25' located centrally thereof. The member 25 may be secured to the anode in any suitable way, as by spot welding or by a simple retaining member (not shown) which is spot welded to the face of the anode and extends over the edge of the disc.

The filamentary cathode 10 is substantially U-shaped and is provided with outwardly extending arms 27 and 28 welded to lead-in wires 13 and 14. The cathode 10 is secured in position by the supporting disc 15, which is in turn secured to the flange 17 of the grid structure 12 by four equally spaced retaining screws 29. As illustrated, the openings 30 through the header or disc 15 provide a clearance around the supporting screws to permit alignment of the filamentary cathode 16 with the center of the grid aperture 22. A hollow cylindrical insulating shield 31, preferably of mica, is inserted within the lower end of the grid assembly 12 and surrounding the lower end of the filament 10 and the lead-in 'conductors 13 and 14 to prevent the deposit of conducting material on the grid structure which would tend to cause electrical leakage between the insulated grid segments. The electron gun assembly as shown is not vacuum tight and is intended to be used within an envelope structure which may be either the neck portion of a conventional cathode ray tube or it may be mounted within the vacuum housing of an electron beam recorder of the type shown,

for example, in my Patent No. 3,116,962, granted Ian. 7, 1964.

In a particular embodiment of my invention the gun operates at a beam voltage of about 10 kv., with a beam limiting apertur of 1 mil, with a beam current of about 10 microamps through the aperture and l milliamp collected at the anode. In that embodiment the following gun dimensions were employed: the filamentary cathode was of cathode tungsten wire about .008 inch in diameter and the width of the hairpin had a maximum dimension of about .025 inch; the opening in the grid was about .060 inch and the end of the filament terminated about .007 inch short of the end of the opening 22 in the grid structure 12; the hemispherical portion of the grid had a diameter of about of an inch and the conical portion of the anode terminated substantially even in a longitudinal direction with the end of the grid assembly. The filament was heated by direct current of about 6 amperes resulting from a voltage in the order of 1 volt impressed across a mid tapped resistor 32 which provides a cathode terminal 33 for connection with the 10 kv. terminal of the anode-cathode supply illustrated generally by a tapped resistor 34. The anode is operated at ground potential. As is illustrated, the supply 34 provides essentially 10.5 kv. total voltage and the 500 volts negative with respect to the cathode is employed for energizing the segmented grid through conductors 35 and 36 in a manner more readily described in connection with the schematic showing of FIG. 3.

As shown in FIG. 3, the grid structure as a whole is arranged to be energized at a voltag intermediate the adjustable taps 35 and 36 which are mechanically coupled for movement together and, as illustrated, may be adjusted from to about 500 volts negative with respect to cathode voltage. This voltage is applied to a network of resistors 37, 38, 39 and 40 which are essentially connected in parallel with their physically outer terminals connected to tap 35 and their common inner terminals connected to tap 36. Jointly movable taps 41 and 42 are mechanically connected together as indicated schematically at 43 and are connected electrically respectively with opposed grid segments 18 and 20. In a similar manner adjustable taps 44 and 45 are mechanically connected as shown at 46 and are movable together and are electrically connected to opposed grid segments 19 and21. With all four taps at the middle positions of the resistors 37-40, respectively, the grid segments are, all energized with the same voltage, which is halfway between the voltage of taps 35 and 36. The intensity of the electron beam is adjusted by moving the taps 35 and 36. Centering of the beam is accomplished along one axis by moving th contacts 41 and 42 on resistors 37 and 39 so that the voltage of one grid segment is increased by the same amount that the opposed grid segment is decreased. In a similar way the beam is centered along an orthogonal axis by moving the taps on resistors 38 and 40 in the proper direction. Thus it is seen that the opposed grid segments are energized by voltages which are above and below the average grid voltage by equal amounts. Thus the centering adjustment does not afiect the intensity and also has a negligible effect on focusing since the voltage at the center of the grid aperture 22 is eifectively that determined by the intensity control as established by taps 35 and 36.

With the structure described and illustrated and the circuit for energizing it it is possible to accurately center the electron beam in the fine beam limiting aperture without the necessity of excessive care in the making of the gun parts or in the assembly operation. This results in improved Operation and lower cost of manufacturing.

While I have illustrated and described a particular embodiment of my invention, it will be apparent to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects and I aim, therefore, in the appended claims to cover all such changes and modifications as fall Within the true spirit and scope of my invention.

4 r What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electron gun for producing a focused beam of -and including an opening therethrough for the passage of electrons and a plurality of mutually insulated segments surrounding said opening, said grid electrode having a substantially hemispherical shape facing said anode and said anode having a portion of gradually reducing transverse cross section in the direction of said grid.

3. An electron gun comprising a cathode, an anode having a beam limiting aperture therein and a grid structure interposed therebetween and adjacent said cathode including a plurality of mutually insulated segments sur I rounding an opening for the passage of electrons, means for energizing said grid structure to control the intensity of the electron beam, and means for adjusting the relative voltages of the opposed ones of said segments above and below the voltage for controlling the intensity of the electron beam to center the beam in said beam limiting aperture.

4. An electron gun comprising a cathode, an anode having a beam limiting aperture therein and a grid structure interposed therebetween and adjacent said cathode including four mutually insulated segments surrounding an opening for the passage of electrons, means for energizing said grid structure with a direct current Voltage to control the intensity of th electron beam, and means for adjusting the relative direct current voltage of the, opposed ones of said segments aboveand below the'voltage for controlling, the intensity of the electron beam to center the beam in said beam limiting aperture.

References Cited UNITED STATES PATENTS 2,784,334- 3/1957 Barnett 313.-59 2,976,457 3/1961 Reisuer 3l5.3l 3,178,603 4/1965 Moss 3 13.86

JAMES W. LAWRENCE, Primary Examiner. DAVID J. GALVIN, Examiner. V1 LAFRANCHI, Assistant Examiner. 

1. AN ELECTRON GUN FOR PRODUCING A FOCUSSED BEAM OF ELECTRONS COMPRISING A FILAMENTARY CATHODE, AN ANODE HAVING A BEAM DEFINING APERTURE THEREIN, AND A GRID ELECTRODE STRUCTURE INTERPOSED BETWEEN SAID ANODE AND CATHODE AND INCLUDING A PLURALITY OF MUTUALLY INSULATED SEGMENTS DEFINING AN OPENING THERETHROUGH FOR THE PASSAGE OF ELECTRONS, THE END OF SAID CATHODE BEING RECEIVED WITHIN SAID OPENING. 